The invention relates to a derrick, in particular a drilling rig derrick, comprising a derrick structure, and lifting tackle for a load, for instance, a drill string, in the derrick structure.
An essential function in a drilling rig derrick is vertical movement of loads, primarily the drill string and its sections, and lowering and retrieving equipment, for example a BOP (blowout preventer), with the aid of a drill string.
Drawworks, wires and blocks are used in conventional drilling rig derricks. More recently, drilling rig derricks have been produced where the load handling takes place with the aid of hydraulic cylinders in combination with wires and blocks. There are also known proposals to use driving gears having a motor or motors coupled to gearwheels which climb on vertically mounted racks in the derrick.
The last-mentioned solution has the advantage over wire systems that the wire as a load-bearing element is eliminated. A wire will stretch under load. In today""s wire systems in drilling rig derricks it is therefore necessary to monitor the wires and replace them at regular intervals in order to maintain the desired precision in the lifting tackle.
A problem in connection with the art using driving gears with motors/gear boxes coupled to gearwheels which engage with racks is that motors having gear boxes/gearwheels climb along the rack, thus requiring the power supply to be provided by means of a flexible hose or cable and the weight of the motors or driving gear to be lifted in addition to the load that is lifted.
The last-mentioned disadvantage can be obviated by making the lifting tackle in such manner that it is not the driving gear which climbs up along the racks, but the racks which are moved up and down by the driving gear.
There are known devices for movement, especially hoisting and lowering of loads, using a driving gear which includes a gearwheel in engagement with a rack that is divided into successive and hingedly interconnected rack segments which run in a guideway, see for example U.S. Pat. No. 1,870,244, U.S. Pat. No. 1,916,517 and U.S. Pat. No. 2,170,595.
In these known devices, the rack segments are locked in the straight, vertical lifting line, and the lifting devices involved are intended for relatively short lifting or jacking lengths. The rack segments are stored horizontally.
It is an object of the present invention to provide a lifting/driving device which is intended for practically endlessly long travel, and almost unlimited capacity in terms of running power and speed.
A particular object of the invention is to provide a lifting device having rack segments which can be moved up and down with the aid of a driving gear and where the rack segments in the vertical, load-bearing straight line are prevented from buckling/bending.
It is also an object of the invention to provide a derrick, in particular a drilling rig derrick, where the load handled by the lifting tackle is taken up at the bottom of the derrick.
It is also an object of the invention to provide a derrick, in particular a drilling rig derrick having a lighter and simpler structural design, where the derrick structure is primarily proportioned for horizontal forces.
A particular object of the invention is to provide a drilling rig derrick for use on board a floater, for example, a drilling ship, which derrick has a centre of gravity that has been lowered radically in comparison to conventional drilling rig derricks.
A particular object of the invention is also to provide a drilling rig derrick where the lifting tackle, as occasion requires, can be used to press the drill string or pipe string.
It is also an object of the invention to provide a derrick, especially a drilling rig derrick, which can be extended according to need in a simple manner.
These and other objects of the invention are attained with a derrick, especially a drilling rig derrick, including a derrick structure, and lifting tackle for a load, for example, a drill string, in the derrick structure, which derrick is characterised in that the lifting tackle comprises vertical guideways in parallel relation, each including a vertical main guide rail, a storage guide rail parallel thereto, and a connecting guide portion between the two said rails arranged in a lower portion of the derrick, a rack slidably mounted in each guideway, which racks are divided into successive, hingedly interconnected rack segments designed to bear against one another when the rack or a part thereof is in the vertical main guide rail, said main guide rail being adapted for horizontal support of the rack segments, a load-bearing yoke supported by racks in the respective vertical main guide rails, and a driving gear including a driving gearwheel in driving engagement with the racks in the respective vertical main guide rails.
Advantageously, the racks may have teeth on two parallel sides.
A lifting tackle according to the invention can in practice be designed so as to be a very precise mechanism. The load will be taken up at the bottom of the derrick, where the driving gear is located. This gives the possibility of a lighter (in terms of weight) derrick structure, where the taking up of horizontal forces is given importance.
Because the load is taken up at the bottom of the derrick, and because the derrick can be built so as to be lighter, the centre of gravity of the derrick will be lowered, which is important and represents a great advantage when used on board floaters, for example, drilling ships.
Advantageously, the lifting tackle may also be used to press, for example, a pipe string. when the load-bearing yoke is connected to the racks.
Initially, the lifting height will be determined by the number of rack segments. The rack segments which do not form a part of the vertical, supporting rack, will be stored in the vertical storage guide rail.
The rack segments can be made so as to rest on top of one another on straight surfaces, and the horizontal support results in their being prevented from buckling/bending.
The derrick structure can be extended or shortened in a simple manner by adding or taking away a derrick segment.
When needed, additional rack segments can be inserted into the rack segment train, or optionally taken out.
The connecting portion between the main guide rail and the storage guide rail may be made in the form of a curved guideway portion, but it is especially advantageous if the connecting portion can include an idler wheel pivotally supported about a horizontal axis and having a periphery in contact with the rack segments which are in the connecting guide portion. It is particularly advantageous if the idler wheel has an elastic peripheral coating, for example, of a suitable rubber material.
An idler wheel of this kind will provide favourable transport of the rack segments in this U-shaped portion of the guideway. The elastic peripheral coating gives smooth contact between the idler wheel and the rack segments and serves to take up smallish dimensional deviations and will prevent jerking and a tendency to swinging motions in the segment train formed by the rack segments.
It is especially advantageous if each individual rack segment is made in the form of an H-beam, with teeth on the parallel flange sides of the H, whereby smooth drive actuation of the rack segments can be obtained with the aid of driving gearwheels which act on both sides of the rack segment.
It is particularly advantageous according to the invention if synchronisation is employed which includes gearwheels that are in engagement with the rack in the storage guide rail and are capable of drive connection with gearwheels that are in driving engagement with respective driving gearwheels in the driving gear. This makes possible a synchronisation of the movements of the rack segments in the two vertical guide rails.
According to the invention, there may be provided a tension adjusting device which serves to tension the rack segments against the idler wheel, so that a desirable and favourable abutting interaction is obtained between the periphery of the idler wheel and the rack segments in this portion of the guideway.
The gearwheel that is in mesh with the rack in the storage guide rail may be supported so as to be position-adjustable, to allow a tensioning of the interaction between the rack segments and the idler wheel, or more advantageously: the idler wheel may be adjustably supported for such tensioning.
The drive connection between the respective gearwheel which is in engagement with the rack in the storage guide rail and the gearwheel which is in driving engagement with a respective driving gearwheel, advantageously includes a universal shaft and optionally shaft couplings.
It is particularly advantageous if the driving gear according to the invention includes a driving motor for each driving gearwheel.
To secure synchronous operation of the driving motors, it is of advantage if directly opposite motors in the driving gear are drive-connected by means of a respective drive shaft.
In the case of a drilling rig derrick that is to be used on board a floater, it will be necessary to include a heave compensator in the lifting gear. Such heave compensation can, according to the invention, be obtained by allowing each rack to be attached to at least one driving gearwheel which is drive-connected to an electromotor and at least one driving gearwheel which is drive-connected to a hydraulic motor, which hydraulic motor is connected to a hydraulic accumulator connected to a hydraulic accumulator system having a low pressure feed pump. The arrangement may be so designed that is when a hoist load moves downwards the hydraulic motors act as pumps and charge the accumulators and when the hoist load moves upwards act as motors, power being drawn from the accumulators.
The racks will often, for example, in a drilling rig derrick, be in a tough environment and it will therefore be advantageous to have guideways which are shielded from the environment, whilst the guideways are designed for shielded movement of the load-bearing yoke in the main guide rails.
According to the invention, the shielding of the load-bearing yoke may include a respective canvas element actuated by the load-bearing yoke wherein there are embedded magnetically actuatable particles, magnets being mounted on the main guide rail to hold the canvas element in place on the main guide rail so that it covers the guideway
In a preferred embodiment, rollers are provided on the load bearing yoke which interact with the canvas element and force this away from the guideway, or put it in place again when the load-bearing yoke moves along the guideway.